Two factor authentication systems rely on a shared secret. I can't see how that could be done security in an anonymous decentralized network.

An encrypted file can't be accessed without the decryption key. You could give the file to unauthorized users and the contents of the file would still be secure (to the limit of the strength of the algorithm and key). There is no way to "bypass" this. Math protects the contents of the file. 2FA on the other hand is just an authentication mechanism it can be bypassed. Take blockchain.info as an example, if an attacker (or employee) gained access to the server they could simply download the wallet files. They would still be protected by the password (key) but there would be no need to defeat the 2FA. 2FA relies on trust, it relies on the gatekeeper limiting access. In a decentralized system the attack is also the gatekeeper and they could simply ignore that trust.